1. Field of the Invention
The present invention relates to a method for forming a large-sized spherical wave in which a plurality of limited plane waves are formed by waves transmitted from a respective one of a plurality of elements in a linear transducer based on a predetermined delay pattern and the plurality of the formed limited plane waves are superposed.
2. Description of the Related Art
A linear transducer is comprised of a plurality of elements, which transmit waves to a certain object and receive waves reflected from the object. In the case that height of each element is much larger than its width, the shape of the wave transmitted from each element is not nearly varied in the direction of its height. Thus, the travelling direction of the wave transmitted from the element is considered on the two-dimensional plane. In addition, the shape of the transmitted wave is varied according to the width of the element, in which case if the width of the element is very small the transmitted wave has a shape close to a spherical wave.
There are a dynamic focusing and a synthetic focusing in the focusing types for transmitting/receiving waves. In the case of the dynamic focusing, a transmit focusing is performed by applying a delay time to a respective one of elements and then transmitting a respective wave, and a receive focusing is performed by receiving the reflected wave and compensating for the applied delay time. Meanwhile, in the case of the synthetic focusing, a respective individual clement transmits and receives a wave, to thereby perform a focusing on a memory in a linear transducer.
However, since the wave transmitted from each clement is small in size in the case of the synthetic focusing, it does not travel up to a remote distance, by which reason a ratio of signal to noise is not good.